The present invention relates to the construction of large diameter mining shafts having a diameter in excess of 10 feet and extending to a depth of at least 2,000 feet for use in conjunction with the mining of mineral deposits.
Mining shafts have been constructed in connection with the mining of minerals to serve as access shafts to the mineral deposits and/or as air shafts to the underground mining tunnels. In both cases, such shafts have conventionally been constructed by what essentially amounts to a digging type technique. Typically all such shafts are constructed to extend along a vertical alignment which generally decreases sinking, maintenance and hoisting cost. The shafts can be constructed along an incline where necessary in order to decrease the distance for horizontal cross-cuts and for obtaining access to the layers of mineral deposits.
In sinking a shaft in rock, the shaft is typically formed by drilling various small holes which are then filled with a blasting material for blasting out the rock. This operation is followed by mucking, hoisting the broken rock and establishing ground support. Occasionally during this construction operation various sections of the shaft will be exposed to water permeable rocks thereby enabling water to sink into the shaft. Such water can be removed by the use of large pumps or by drilling holes down the side of the shaft being constructed and then filling such holes under high pressure with a cement mixture. In this manner the shaft is encircled by the cement mixture which penetrates the permeable rock surrounding the shaft so as to decrease the flow of water toward the shaft. Such an operation is occasionally referred to as cementation.
In sinking a shaft in soft ground, the operation first starts with driving either wood or steel spilings around the perimeter and ahead of the bottom of the shaft. The ground is then removed and a permanent wall support is installed. Next, a shaft lining material formed of wood, steel or concrete is constructed in the soft ground after which by way of a digging operation the earth is removed. Next, grout can be forced into the surrounding ground for reinforcing the side walls of the shaft.
In constructing relatively small holes within the earth such as in oil and gas well drilling, bore holes on the order of 60 inches in diameter have been drilled. Exemplary of drilling techniques and equipment used for such purposes is the apparatus described in U.S. Pat. No. 4,133,397. This patent also indicates that such equipment can be used in various mining and foundation forming operations. In the operation of the drilling system disclosed in such patent, the drill bit is rotated by a rotary drive mechanism while drilling fluid is circulated for cooling the drilling bits and for flushing cuttings from the cutting surfaces of the drilling bits and from the bore hole being drilled.
U.S. Pat. No. 4,102,415 also discloses an earth and rock bore drilling system for forming vertical shafts for mines or other subterranean installations. This patent discloses a conventional fluid circulation mechanism of the general type shown in FIG. 1 in the present application. This type of conventional fluid flow mechanism can be used in the drilling of relatively small bore holes. Such a circulation system, however, does not provide for an efficient or really practical operation in drilling large bore holes, i.e. holes in excess of 10 feet in diameter.
Various attempts have also been made at conducting drilling operations between various tunnels underground; exemplary of such attempts are the embodiments illustrated in U.S. Pat. Nos. 3,167,354 and 4,123,109. In addition, some attempts have been made at subterranean hydraulic mining of mineral deposits such as shown in U.S. Pat. Nos. 3,874,733 and 4,092,045. Furthermore, with respect to the process of mixing the mineral deposits, such as coal, in a slurry for the purposes of transportation along a pipeline, such techniques are shown in U.S. Pat. Nos. 3,041,053 and 3,924,895.
With the increasing necessity for economically and efficiently obtaining sources of energy, it has become even more critical for finding new techniques for use in the mining of minerals. Such problems are especially enhanced in light of the safety considerations in constructing mining shaft with conventional blasting and digging techniques.